Palladized asbestos

Conformation 8 agrees with the chemical transformations of sophoridine obtained earlier (203). Matrine isomers are known to react faster by dehydrogenation over palladized asbestos or with mercuric acetate if they contain cis hydrogens. Sophoridine has been shown to dehydrogenate faster than allomatrine (5), but slower than matrine (4) (196). Since there are three cis hydrogens (H-5, H-6, H-7) in matrine and none in allomatrine, the sophoridine molecule is supposed to contain two cis hydrogens a cis orientation of H-6 and H-7 in 8 meets this requirement. 

Representative compounds having a pyrrolidine or piperidine nucleus have been dehydrogenated in benzene solution under pressure at 250-350° over a nickel catalyst, e.g., l-( -amyl)-pyrrolidine to l-( -aniyl)-pyrrole (88%), indoline to indole (75%), and 1,2,3,4-tetrahydrocarbazole to carbazole (95%). Indole is also prepared by the dehydrogenation of its 2,3-dihydro derivative over palladium in boiling xylene (62%)." Partially hydrogenated alkylpyridines are dehydrogenated over palladized asbestos." 2,4-Diphenylpyrrole is synthesized by the selenium dehydrogenation of its 2,3-dihydro compound (46%). ... 

Zelinsky and Borisoff give the following directions for preparation of platinized or palladized asbestos catalysts 140... 

In this case also, charcoal was the only successful catalyst under the moderate conditions of temperature used. Negative results were obtained with platinized asbestos, palladized asbestos, nickel (supported on silica... 

Palladized asbestos is prepared in exactly the same way as platinized asbestos (see p. 1563). 

Prior to this synthesis, Pictet and Finkelstein (22) had attempted a synthesis of the alkaloid by way of its 3,4-dihydro derivative but were unable to remove the two extra hydrogen atoms from its pyridine ring. Spath and Burger (19) completed this synthesis by dehydrogenating 3,4-dihydro-papaverine with palladized asbestos at 200°. Homoveratrylamine and homoveratroyl chloride were condensed, and the amide (XXXIII) converted to 3,4-dihydropapaverine (XXXIV) by a Bischler-Napieralski iso-... 

Palladized or platinized asbestos (or Deoxo unit) Removes traces of 02 from H2 at room temperature, removes 02 from inert gases at... 

The experiments of Zelinsky and Borisov (21) appear to substantiate that piperidine is the intermediate. A high yield of it was obtained in a flow type hydrogenation of pyridine in the presence of palladized or platinized asbestos. A similar flow type reaction with the same catalysts (22) gave not only piperidine, but side products which the investigators suggest might be 1,2,3,4-tetrahydropyridine and 1,2,5,6-tetra-hydropyridine (2-piperideine). The observation, however, needs further confirmation. Reinvestigation of the products of reaction with modern... 

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